Suburb guide · 2099
Can I build a duplex or granny flat in Dee Why?
Dee Why sits in Northern Beaches Council's area under Warringah Local Environmental Plan 2011. We ran 25 real Dee Why addresses through the checker: the typical block is 662 m² with 15.0 m of frontage, 16 of the 25 could add a granny flat, and 14 could carry two separate homes today.
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The typical Dee Why block
The middle block of the 25 we checked is 662 m² with 15.0 m of street frontage. The smallest was 305 m² and the largest 1,369 m². Zones in the sample: R2 (17), R3 (5), E1 (1), MU1 (1), RE1 (1).
The 25 blocks we checked, by land size.
What homes sell for in postcode 2099
Median sale prices for the whole of postcode 2099, January to March 2026. These cover every suburb sharing the postcode, not Dee Why alone, and they are not a value for any one block.
- Houses: $2.92m (39 sales)
- Units and apartments: $1.10m (116 sales)
Source: NSW Government Rent and Sales Report (Department of Communities and Justice), sales tables by postcode, NSW Government. Updated each quarter.
A granny flat
16 of the 25 blocks we checked could take one. Warringah LEP cl 5.4(9) — the greater of 60 m² or 11% of the house’s total floor area, parking excluded. Separately, the state Housing SEPP allows a granny flat of up to 60 m² through the ten-day complying-development route on a lot of 450 m² or more with a 12 m frontage, where the land is not flood, bushfire or heritage constrained.
Dual occupancy (duplex) rules in Dee Why
14 of the 25 blocks we checked could carry two or more separate homes today.
Under Warringah Local Environmental Plan 2011 a dual occupancy needs 800 m² — this LEP sets no frontage minimum, so Council's DCP governs width.
Only 5 of the 25 blocks we checked were ordinary R2 land outside the Low and Mid-Rise area, which is too few to read anything into — most of Dee Why in our sample was zoned or mapped some other way.
Low and Mid-Rise
18 of the 25 blocks sat inside the state Low and Mid-Rise area — within about an 800 m walk of a listed centre or station. Inside it the Housing SEPP overrides the LEP minimums: a dual occupancy on 450 m² with a 12 m frontage, terraces on 500 m² / 18 m, townhouses on 600 m² / 12 m and a manor house on 500 m² / 12 m, up to 9.5 m. That is what lifts the two-homes figure above; a block one street outside the line gets the LEP figure instead.
What else turned up
2 of 25 were on bushfire-prone land. Any of those takes a block out of the fast-track routes and into a full DA, so it changes the answer more than the lot size does. Northern Beaches has no flood layer on the Planning Portal, so flood is checked against Council’s own study by hand.
How we got these numbers
We took 25 real Dee Why street addresses from the NSW geocoder and ran every one through the same engine this site runs for you, reading the planning controls live. Nothing here is modelled or estimated.
It is a sample, not a census. The addresses are a spread across what the geocoder returns, so treat these as "of the 25 blocks we checked" rather than a figure for every block in Dee Why. Your own block is the only one that answers for itself — that is what the box on the right is for.
Enter the address — lot, frontage, zone, constraints and what it can carry.